Not applicable.
Not applicable.
The invention relates to a device for beam guiding a laser beam, with at least one optical element, which with a retaining is positioned with respect to a supporting section of a housing.
Laser technology is used in very varied fields. For example, CO2 lasers, e.g. square-folded or coaxial CO2 lasers, are used for flexible material processing.
Square-folded resonators have been developed for increasing the power; in them, based on the folding of the light path, a long discharge path is provided in spite of a compact structure. Optical elements for beam guiding are provided at the end of the discharge path, and are positioned on housing sections.
In coaxial CO2 lasers, unstable resonators are concerned, with an annular discharge space which has, for example, toroidal optical elements for beam guiding.
The optical elements used for beam guiding are differently constituted in transmittance and reflectance, in dependence on their function. Optical elements are used which make total reflection possible, and also optical elements which make possible a partial transmission with different transmittances.
In square-folded CO2 lasers, a device for receiving the optical element has heretofore been used, which has a first annular member for mounting the optical element, arranged on the vacuum side of the laser path. The optical element is positioned relative to the annular member by means of an intermediate member which surrounds the optical element in the radial direction. A retaining member is set on the intermediate member and connected to it, and fixes the optical element axially of the first annular member. The intermediate member is first fixed to the annular member by screw connections. The retaining member is then likewise fixed to the annular member by tightening screws which pass through the intermediate member. This arrangement is very time-consuming in the assembly of the optical element and requires high precision in the production of the components. A non-uniform application of force to the optical element can result from the fixing of the retaining member to the ring member by means of tightening screws, due to a different tightening torque of the tightening screws, so that distortions arise in the optical element. At the same time, the distortions of the screw securement lead to unevenness of the seating surface of the optical element, resulting in a smaller heat conduction from the optical element into the ring member. A deformation of the optical element follows from the unevenness of the seating surface. Heat can be transferred out of the optical element more poorly because of the smaller contact surface as against an ideally flat seating surface, and the beam quality is worsened.
In coaxial CO2 lasers with their unstable laser resonators, the laser radiation is coupled out by means of a gap in an annular mirror. The laser beam leaves the vacuum chamber through a transmissive optical element which forms the closure of the vacuum chamber. If the sealing of the optical element takes place e.g. by soldering, the soldered joint is exposed to a temperature change stress when the laser is operating. This has the consequence that the joint can become leaky in the course of time.
The invention now has as its object to provide a device for beam guiding a laser beam with at least one optical element which has a planar seating surface for complete seating of the optical element and also makes possible a simple and rapid, and also stress-free, assembly of the optical element.
This object is attained by a retaining element, a support section of a housing section, at least one optical element which with the retaining element is positioned with respect to the supporting section, a clamping element that fixes the optical element to the supporting section of the housing section, a fastening section on the housing section having the supporting section, on which the clamping element engages for central force introduction of a retaining force and at least one retaining element interpositioned between the clamping element and the optical element that positions the optical element with respect to the supporting section.
A distortion-free arrangement of the optical element to the supporting section is given by means of a central introduction of a retaining force on the optical element with a clamping element via a retaining element, for seating on a supporting section of a housing section. Furthermore it is thereby made possible to use any optional geometry of an optical element. A specific matching of the device to different beam profiles can thereby be made possible. This matching of the optical element to the beam profile has the advantage that a rapid removal of the heat arising in the optical element due to the absorbed laser radiation is made possible. Deformations of the optical element can thereby be kept small or even prevented.
Furthermore, due to the central introduction of force, the optical element can abut completely on the supporting section, and the flatness of the seating surface can be maintained, so that good heat removal is provided. It is furthermore made possible by the central introduction of the retaining force with a clamping element that s simple assembly of the optical element to the housing section is given. The at least one optical element of the at least one retaining element and the clamping element can be mounted, simply and securely, one after another to the housing section. Since the clamping element has the effect of a central closure, a considerable saving of assembly time can moreover be attained. Furthermore, a reduction of the number of components is provided by the arrangement of a fastening element on the housing section for the clamping element, so that a reduction in production costs is attained.
According to an embodiment of the invention, it is provided that the clamping element is constituted as a screw ring. A clamping element that is easy to manipulate in assembly is thereby provided. The use of the screw ring as the clamping element makes possible a uniformly distributed introduction of force on a retaining element, so that the optical element abuts with a uniform pressing force on the supporting section of the housing section.
According to a further embodiment of the invention, it is provided that a clamping surface is provided between the retaining element and the clamping element, and has at least one sectionally annular surface. This embodiment makes possible a reduced frictional moment between the clamping element and the retaining ring, so that a transmission of the axial force without at least partial rotation of the retaining element is made possible, whereby the optical element is pressed against the supporting section without any change of its previously fixed position.
According to a further embodiment of the invention, it is provided that the retaining element has a stop surface as a mounting safeguard. Thereby, when a maximum torque for the tightening of the clamping element is exceeded, a safe mounting of the optical element can be provided. Since the retaining element abuts on the optical element via a seal or a sealing damping element, a distortion-free positioning of the optical element on the supporting section is provided. Alternatively, it can also be provided that the stop surface is arranged on a housing section or further component.
According to a further embodiment of the invention, it is provided that the supporting section of the housing is produced by turning or milling with diamond, polycrystalline diamond (PKD), ceramics, and also by grinding, precision turning, or lapping. Due to the low roughness thereby attained, the supporting section has a higher contact surface between the optical element and the supporting section, leading to an improved heat removal. Furthermore, a high degree of flatness, for example less than 10 xcexcm, preferably less than 1 xcexcm, can be attained by this treatment, so that the lost power, which is reflected in a heating of the optical element, is reduced.
Furthermore, it is provided that a seal or a sealing damping element is arranged between the retaining element and the optical element, so that a sealed arrangement is provided between the optical element and a housing section surrounding the optical element, or a section of the retaining ring, surrounding the optical element. Simultaneously, a sufficient pressure of the optical element on the supporting section can be maintained due to the resilient effect of the seal, in order to ensure a good removal of heat.
A further embodiment of the invention provides that the optical element is constituted of diamond, zinc selenide, gallium arsenide, silicon or copper. The material for the optical element can be chosen according to the purpose for which the device is to be used, the laser type, and the laser power. For example, silicon is used in a square-folded CO2 laser as the deflecting mirror up to 4 kW, and copper for a higher power range. Zinc selenide is preferred as the coupling-out mirror in a square-folded CO2 laser. In coaxial CO2 lasers, zinc selenide can be used at low powers, or diamond at all power ranges, as the material for the optical element.
In the design of an optical element departing from a round diameter in the outer contour, it is provided that the optical element is fixed by a frame in a position coincident with the exit opening in the housing section. By this means, the optical element can completely cover the exit opening and the region of the optical element abutting on the seating surface is preferably equal in amount in all directions. A uniform heat removal can thereby be provided.
According to a further embodiment of the invention, it is provided that a seal is respectively provided between the housing section and the frame, and also between the optical element and the frame. A vacuum-tight arrangement can thereby be provided in a simple manner. A simplification in assembly can be provided by the separated design. In addition, an increase of the degree of sealing can be made possible.
According to a further embodiment of the invention, it is provided that the optical element has an outer contour matched to the beam profile and preferably rectangular, banana-shaped, or the like and in particular made of diamond. This form of embodiment is particularly advantageous when used for coupling a laser beam out of a coaxial CO2 laser. By matching the geometry of the optical element to the coupled-out beam profile, the production costs of the optical element can be reduced, particularly when diamond is used. At the same time, the heat arising from the absorbed laser radiation can be directly carried away via the seating surface into the housing section. Furthermore, good airtightness can be attained by the application of a central retaining force over the clamping element, and the separation of the force transmission to a retaining element, even with non-circular geometry of the optical element.
Industrial diamonds are preferably used. Due to the high thermal conductivity of diamond, the heat that arises in the optical element from the absorbed laser radiation can be carried away very rapidly into the cooled housing. Furthermore, a low thermal expansion and a high mechanical strength are given. The optical element can thereby substantially retain its initial shape. Diamond furthermore has a long lifetime, even under high power. With unstable resonators, as is the case with coaxial CO2 lasers, the laser beam after leaving the vacuum chamber is shaped by mirrors and by a diaphragm. The focus of the laser beam must here be situated in the diaphragm. Excessive heating of the optical element and a resulting deformation would give a deflection of the exiting laser beam or a focus displacement in the beam direction. This could lead to damaging the diaphragm in the beam telescope and can be prevented by the advantageous embodiment.
According to a further embodiment of the invention, it is provided that the retaining element has an inclined surface surrounding and abutting the seal, and fixing the seal at least in the direction of the optical element, which preferably has a round outer contour, and/or at least radially outward. It is thereby made possible that a sealing effect toward the vacuum side of the housing section is attained.
It is provided, for round optical elements, that the seal is constituted as an O-ring seal which has an external diameter equal to or greater than that of the housing section, or section of the retaining element, immediately surrounding the optical element. The optical element can thereby be retained by means of the seal in a preassembled position after insertion. Furthermore, it is thus made possible that the retaining element and the seal do not rotate during the application of the retaining force and that the retaining element only executes a motion in the axial direction, directed toward the optical element. By means of the seal abutting directly on the housing section, a frictional moment is given toward the housing section and on the inclined surface, after the insertion of the retaining element, and is greater than the frictional moment between the retaining element and the clamping element. The rotational motion of the clamping element can thereby be converted into an axial motion of the retaining element.